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Scott Laurila ~ Senior Application Engineer
Greenheck Fan Corporation
Schofield, Wisconsin
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gen a
Properties of Air The Ps chrometric
Chart
ApplicationsMixed Air
Cooling
Dehumidification
Energy Recovery
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ourse ec ves
At the completion of this session, you should be able to use aPsychrometric Chart to:
ent y t e propert es o a r at a g ven state con t on
Illustrate the performance characteristics of basic heating
Demonstrate how the use of Energy Recovery devices can
reduce heating and cooling loads in building designs
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syc rometrcs
Psyc rometr cs s t e sc ence ea ng w t t e p ys ca
laws or air water mixtures
Important in the design of HVAC systems as numerous air
properties can be found over a broad range of conditions
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ropertes o
Dry-Bulb Temperature
Wet-Bulb Temperature
Dew-Point Temperature
Relative Humidity
Humidity Ratio
Enthalpy
If any two of the above properties are known, the
properties
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Dry-bulb temperature is the
temperature read from astandard thermometer
heat energy at the given
condition
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from a thermometer with the
bulb covered by a wet wick
"Sling Psychrometer"
Difference between dry-bulb
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dryness of air
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ropertes o
Dew-point temperature is thetemperature at which
condenses on objects
When the dry-bulb, wet-bulb,and dew-point temperatures
are equal, the air issaturated
saturated
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ropertes o
Relative humidity is the measure of how much moisture the airis holding versus how much moisture the air can hold at a
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Expressed as a percentage
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moisture the air can hold increases
Relative Humidity = moun o mo s ure e a r s o ngAmount of moisture the aircan hold
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ropertes o
Humidity Ratio is a measure of the weight of water in a givenamount of air
so re erre to as pec c um ty
Can be expressed ingrains
,
Humidity Ratio = oun s o mo s urePounds ofdry air
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e syc rome rc ar
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aturaton urve
Saturation Curve
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ry- u emperature
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e - u emperature
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ew- o n empera ure
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e a ve um y
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H mi it R ti
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ens e an a en nergy
Sensible Energy is the heat that causes changes in the air's drybulb temperature
atent nergy s t e eat assoc ate w t p ase c ange. t s
representative of changes in the air's moisture content with no
change to the dry-bulb temperature
Enthalpy is the total energy in a given amount of air at its
present conditions
Enthalpy (h) = Sensible Energy + Latent Energy
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nt a py
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syc rometrc art econstructe
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Example:
93F DB, 65F WB
Find: n a py
Dew-Point = 50.9F
Relative Humidity = 24.0%
Wet-BulbDew-Point
Hum. Ratio = 66.8 grains/lb dry air
Enthalpy = 32.9 Btu/lb
Humidity Ratio
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Dry-Bulb
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r ens y orrec ons
Do NOT forget about elevation! Above 2,000 feet elevation, the air density is reduced by
approxma e y . per every , ee
A change in air density also changes the physical and-
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syc rometrc rocesses
Air ConditioningMixed Air
Cooling Coils
Reheat
Energy Recovery
Sensible Devices
Total Enthalpy Devices
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Evaporative
Cooling
Steam
Humidification
Example Processes
160
140
80
- -
Latent: Up & down
DesiccantCoolin &
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100
DehumidificationDehumidification
40
50
80
60
40Heat
3020
20 30 40 50 60 70 80 90 100 110
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Dry Bulb Temp.
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Use the ASHRAE indoor
n oor es gn on tonses gn con t ons to e p w tprocess calculations
75F, 50% RH
Winter Indoor Design
72F, 35% RH
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xe r on ons Step 1: Identify outdoor condition, indoor condition, and
ventilation rate (% outside air)
Step 2: Draw a straight line between the outdoor and
Step 3: Draw a straight line between points 1 and 2
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xe r xampeOutdoor Air: 95F DB/75F WB
Room Air: 75F DB, 50% RH
Ventilation: 25% Outdoor Air
95F x 0.25 = 23.75F75F x 0.75 = 56.25F
Mixture = 80F
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Condenseroo ng rocess xampe
Hi h Pressure
CompressorExpansion Valve
vapora or
Low Pressure
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oo ng o rocessesCapacity (Btu/hr) = 4.5 x SCFM x h
oo ng on = , tu r
Capacity (Tons) = 4.5 x SCFM x h / 12,000
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Exercise 2: A customer wants to cool 4,000 SCFM of
oo ng xerc se
outside air from 93F DB / 65 WB to 50F saturated air
Find the following parameters for 50F saturated air:
Property Value Units
Relative Humidity 100 %
Dew Point 50 F
What is the chan e in enthal from 93DB/65WB to
Humidity Ratio 64.8 grains / lb dry ai
Enthalpy 22 Btu / lb dry air
50DB/50WB? h = 10.9 Btu / lb dry air
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e erm ne e coo ng onnage requ re n s process.
Capacity = 16.4 Tons
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Introducing cold, saturated air directly into an occupied
u w
space may be too cool for occupant comfort
Reheat can be used to bring the air to a space-neutral
Reheat Methods
Electric Heat
Hot Water Coil
Hot Gas Reheat
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Condenseroo ng rocess xampe
Hi h Pressure
CompressorExpansion Valve
vapora or
Low Pressure
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ot as e ea
ReheatCoil
Air Conditions After Reheat Coil:
65F DBT/56F WBT (50% RH)
Air Conditions After Evaporator:50F DBT / 50F WBT
Evaporator
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Supply Air
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nergy ecovery
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y nergy ecovery
Economic Benefits
Reduced Initial Costs
e uce pera ng os s
ASHRAE Standards & Guidelines
ASHRAE 62.1 2010 Ventilation for Acce table indoorair quality
ASHRAE 90.1 2010 Energy Standard for Buildings
. Performance Green Buildings
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ASHRAE Standard 62Ventilation for Acceptable Indoor Air Quality
minimize the potential for adverse health effects. Typical ventilation rates:
15 CFM per person for Classrooms
17 CFM per person for Offices
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Steven Taylor Taylor Engineering
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. -
Exhaust Air Energy Recovery (6.3.6)
Supply air is greater than 5000 CFM
70% or more of supply is outdoor air (3500 CFM)
Energy recovery system shall have a total effectiveness
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ASHRAE 90.1-2010
Table 6.5.6.1 Energy Recovery Requirement (IP)
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Standard for Design of High-Performance Green Buildingswww.ashrae.org/greenstandard
Table 7.4.3.8 Energy Recovery Requirement (IP)
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nergy ecovery as c erms
(no moisture) Also referred to as heat recover
Total Energy Recovery transfers both sensible and latent
energy
Effectiveness refers to the efficiency of the energy
recovery device (expressed as a percentage)
Total effectiveness
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ens e eat ecovery Sensible Heat Recover
Aluminum fixed plate Run-around coils
Heat-pipe heat
exchangers
ens e w ee s no
desiccant)
Transfers sensible ener
only (no moisture transfer)
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ens e a e
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Sensible Ener recover
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moves the outdoor air dry
bulb temperature laterally
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140
120
temperature
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60
100
80
60
HeatExchangers
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40 40
20
Room Air
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Dry Bulb Temp.
20 30 40 50 60 70 80 90 100 110
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ota nergy ecovery Total Ener Recover
Enthalpy wheels Enthalpy plates (or cores)
Transfers sensible energy
through the media
rans ers a en energy
through a desiccant (wheel) or
molecular transfer (core)
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nergy ecovery
47Summer Operation w/ Rotary Wheel
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Total energy recovery
160
140
80
shifts OA point towards
RA point
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100Outdoor AirOutdoor Air
-
40
50
80
60
Room Air
30
20
20 30 40 50 60 70 80 90 100 110
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Dry Bulb Temp.
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ar - oa on tons
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E R d C li
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Ener Recover and CoolinPotential
Energy Savings
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Winter O erationWinter O erationSupply Air
Dry Bulb 54F
Humidity 31 grains/lb.
Room Air
(to be exhausted)Dry Bulb 72F
Humidity 41
Outdoor Air
Dry Bulb 0F
Humidity 2
grains/lb.
.
Exhaust Air
Dry Bulb 18F
Humidity 12
grains/lb.
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Wint r r ti nSensible vs. Total ERV
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Possibility of condensation forming whenever a warm, moist
air stream comes in contact with a cold surface
Always consider frost control methods in when winter design
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i h i
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Winter Exhaust Air ProcessSensible vs. Total ERV
Total
Sensible
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Question?
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evew
Psychrometric Charts are useful tool forunderstandin HVAC rocesses
Easily find properties of air across numerous
conditionsAllows us to plot, predict, and calculate the
heating and cooling capacities
An understanding of psychrometrics is thefoundation of energy recovery
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THANK YOU!
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